In-situ fluorinated 2D/3D invert perovskite film solar cell with enhanced ambient stability

Although solution-processed organometal halide perovskites (OHPs) have attracted much attention for solar cell applications due to their superior photoelectric properties, such as strong band-edge absorption, small exciton binding energy, balanced electron-hole transport, superb charge carrier mobility, etc., their instability in the ambient air severely limits their commercial applications. Here, we introduce 4-Trifluorophenyl methylammonium cations (CF3PMA+) on the surface of 3D MAPbI3 films. Subsequently, the hydrophobic fluorinated 2D perovskite thin film is in-situ formed on 3D MAPbI3 surface. The van der Waals interaction between water molecules and the surface of the fluorinated 2D perovskite becomes weaker, which prevents the water molecules from entering the perovskite lattice and, therefore, improves the moisture resistance of the perovskite. In addition, the lifetime of the excited photocarriers becomes longer after 4-Trifluorophenyl methylammonium iodide (CF3PMAI) modification, which is conducive to carrier extraction and interface transport. The 2D/3D perovskite based solar cell (2D/3D PSCs) finally achieves a PCE of 15.01% by introducing CF3PMAI, and the unsealed PSCs can maintain 90% initial efficiency within 500 hrs. Our approach provides a moisture-resistant 2D/3D perovskite film heterostructure, where the hydrophobic fluorinated 2D perovskite layer acts as a protective layer.